Abstract

Background Pulmonary arterial hypertension (PAH) is a fatal condition characterized by progressive vascular remodeling in the pulmonary arteries, eventually leading to right heart failure and death. Dysregulated extracellular matrix (ECM) remodeling is central to PAH pathogenesis and represents a potential therapeutic target. Mesenchymal stromal cells (MSCs) have shown promise in preclinical studies; however, the optimal therapeutic window, dosing frequency, and mechanistic basis for their regulation of vascular ECM remain unclear. Methods We employed a monocrotaline (MCT)-induced rat model of PAH to evaluate different MSC treatment regimens, including early administration (day 1 post-MCT), delayed administration (days 7 and 14), and repeated dosing (days 1 and 11). Additionally, we combined in vivo and in vitro approaches to investigate how MSCs modulate the activation of pulmonary arterial adventitial fibroblasts (PAAFs) and influence ECM remodeling. Results Biodistribution studies indicated that MSC retention in lung tissue peaked within 24 h and gradually declined by day 21. A single early dose of MSCs (on day 1) significantly ameliorated PAH progression, increasing the 28-day survival rate, reducing right ventricular systolic pressure (RVSP), improving right ventricular function, and attenuating small pulmonary vascular remodeling, including reductions in medial thickening, excessive muscularization, and collagen deposition. Repeated MSC administration did not provide additive therapeutic benefit. Both in animal models and cell cultures, MSCs effectively suppressed PAAF activation and reduced ECM protein production. This anti-fibrotic effect was mediated, at least in part, via the pathway involving the upregulation of SOCS3 and consequent inhibition of STAT3 phosphorylation. Conclusion Our findings underscore the importance of early intervention in the PAH disease course for MSC-based therapy. MSCs attenuate vascular remodeling and disease progression, possibl